As it turns out (thanks to listener Reggie, who commented below), Snoopy’s doghouse HAS been shown from different angles! From a Sunday strip from January 31, 1954: and this strip, from December 12, 1958, where Snoopy attempts to sleep on top of the house for the first time:

Great episode! Regarding the comments on Peanuts, Snoopy’s doghouse was originally shown from a 3/4 view in many of the strips from the 50s. Schulz did show the entrance and the pitch of the roof. There was a stip where Snoopy tried to sleep on the roof peak while it was still shown from that angle. Another Sunday strip showed Snoopy’s doghouse from several different angles.